Orexins are hypothalamic neuropeptides that play an important role in the regulation of many physiological behaviours such as arousal, wakefulness, appetite, food intake, cognition, motivated behaviours, reward, mood and stress. Orexin A, also referred to as hypocretin 1, is a peptide composed of 33 amino acids and orexin B, also referred to as hypocretin 2, is a peptide composed of 28 amino acids. Both are derived from a common precursor peptide referred to as pre-pro-orexin [Sakurai et al., Cell, 1998 Feb. 20; 92(4):573-85, and De Lecea et al., Proc. Nat. Acad. Sci., 1998 Jan. 6; 95(1):322-7). Orexins bind to two orphan G-protein-coupled receptors, the orexin receptor type 1 (OX1R) and orexin receptor type 2 (OX2R), which are widely distributed in the central nervous system and peripheral organs such as adrenal glands, gonads, and gut. Whereas orexin A binds predominantly to OX1R, orexin B is able to bind to both OX1R and OX2R.
Orexins are involved in the regulation of a wide range of behaviours including for example the regulation of emotion and reward, cognition, impulse control, regulation of autonomic and neuroendocrine functions, arousal, vigilance and sleep-wakefulness states (Muschamp et al., Proc. Natl. Acad. Sci. USA 2014 Apr. 22; 111(16):E1648-55; for a recent review see Sakurai, Nat. Rev. Neurosci., 2014; November; 15(11):719-31; Chen et al., Med. Res. Rev., 2015; January; 35(1):152-97; Gotter et al., Pharmacol. Rev., 2012, 64:389-420 and many more). Dual antagonism of OX1R and OX2R by small molecules is clinically efficacious in the treatment of insomnia, for which the drug suvorexant, [[(7R)-4-(5-chloro-1,3-benzoxazol-2-yl)-7-methyl-1,4-diazepan-1-yl][5-methyl-2-(2H-1,2,3-triazol-2-yl)phenyl]methanone] has been granted marketing authorisation (Kishi et al., PLoS One, 2015; 10(8):e0136910). The sleep-inducing effects of dual orexin receptor antagonists are predominantly mediated via OX2R (Bonaventure et al., J. Pharmacol. Exp. Ther., March 2015, 352, 3, 590-601), whereas the other physiological states such as emotion and reward, cognition, impulse control, regulation of autonomic and neuroendocrine functions, arousal, and vigilance are rather mediated via OX1R.
Due to their sleep-inducing effects, dual OX1R and OX2R antagonists are not suitable for treating disorders related to impulse control deficits as seen in addictions such as substance use disorders, personality disorders such as borderline personality disorder, eating disorders such as binge eating disorder, or attention deficit hyperactivity disorder (ADHD). Therefore, it is desirable to provide an OX1R selective antagonist for the treatment of impulse control deficits.
Orexin receptor antagonists of various structural classes are reviewed in Roecker et al. (J. Med. Chem. 2015, 59, 504-530). WO2013/187466, WO2016/034882 and Bioorganic & Medicinal Chemistry 2015, 23, 1260-1275 describe orexin receptor antagonists.